Magnetic powder applicator

ABSTRACT

A magnetizable powder applicator arrangement in a printing or display apparatus employing for example a magnetizable drum. The powder is attracted to the outer surface of a nonmagnetizable tube which contains therein a rotatable row of bar magnets having like poles adjacent. The divergent flux field set up by the rotating magnets causes the powder to creep along the surface of the tube in a direction opposite the magnet rotation, and onto a ledge of nonmagnetizable material. The ledge is sufficiently close to the drum, yet sufficiently far from the flux field, for the powder to be attracted to the drum surface without disturbing the selective magnetization thereon.

United States Patent Mason et al.

[54] MAGNETIC POWDER APPLICATOR [72] Inventors: Frederick Percival Mason, Burgess Hill; Frank Arthur Oakley Waren, Hove, both of England [73] Assignee: Creed & Company Limited, Hollingbury,

Brighton Sussex, England [22] Filed: Mar. 18, 1970 1211 Appl. No.: 29,330

[ Feb. 8, 1972 Primary ExaminerMervin Stein Assistant Examinerl /eo Millstein Attorney-C. Cornell Remsen, Jr., Walter J. Baum, Paul W.

l-lemminger, Charles L. Johnson, Jr., Philip M. Bolton, Isidore Togut, Edward Goldberg and Menotti J. Lombardi, Jr.

[ 1 ABSTRACT A magnetizable powder applicator arrangement in a printing or display apparatus employing for example a magnetizable drum. The powder is attracted to the outer surface of a nonmagnetizable tube which contains therein a rotatable row of bar magnets having like poles adjacent. The divergent flux field set up by the rotating magnets causes the powder to creep along the surface of the tube in a direction opposite the magnet rotation, and onto a ledge of nonmagnetizable material. The ledge is sufficiently close to the drum, yet sufiicient'ly far from the flux field, for the powder to be attracted to the drum surface without disturbing the selective magnetization thereon.

6 Claims, 8 Drawing Figures PATENTEDFEB 8l972 3640.247

SHEET 1 UPS 5 2 //Y /1 j/ //l /v LQLLC -7- Q M J Inventors FREDERICK PERCIl/Al. MA SON FRANK ARTHUR OAK LE Y WARE/V Agent PATENTEDFEB 8|972 3540.247

SHEET 2 0F 3 Inventors FREDERICK PERC/ VA L MASON FRANK ARTHUR OAKLY NARN Agent PATENTED FEB 8|972 3.640.247

SHEET 3 BF 3 lnvenlors FR6DER/CK PfRC/VAZ MASON FRANK ARTHUR OAKLEY NARL'N MAGNETIC POWDER APPLICATOR This invention relates to a method and apparatus for handling magnetic powder.

SUMMARY OF THE INVENTION According to the invention there is provided a method of transferring magnetic powder along a nonmagnetic surface is a given direction, comprising repeatedly scanning the surface in the opposite direction with a divergent field of magnetic flux, the arrangement being such as to cause somersaulting of the powder in the given direction.

The invention has particular application to magnetic printing and/or display devices. Such devices are well known, and essentially comprise a magnetizable surface, such as the surface of a drum or belt, which is movable relative to a set of recording heads and can be selectively magnetized by the heads in accordance with the matter to be printed or displayed, the surface then being dusted" with magnetic powder which adheres to the magnetized regions, thus forming a powder image. The dusted surface my then be used directly for display of the powder image, or it may be used as a printing element for transferring the image to a further surface such as a paper tape or sheet.

In its application to such devices the invention provides a magnetic printing and/or display device wherein magnetic powder is transferred along a nonmagnetic surface in a given direction by repeatedly scanning the nonmagnetic surface in the opposite direction with a divergent system of magnetic flux, the arrangement being such as to cause somersaulting of the powder in the given direction.

More specifically the invention provides a magnetic printing and/or display device comprising apparatus for dusting the movable magnetizable surface of the device with magnetic powder, the apparatus including a convex nonmagnetic surface extending upwardly form a supply of the powder to a substantially horizontal nonmagnetic ledge adjacent the magnetizable surface, and a magnetic rotor disposed behind the nonmagnetic surface and having its axis of rotation parallel thereto for producing at the nonmagnetic surface a system of magnetic flux which is divergent in a plane perpendicular to the axis of rotation, the arrangement being such that rotation of the rotor in a given direction causes a layer of magnetic powder to creep in the opposite direction up the nonmagnetic surface and across the ledge by somersaulting of the powder as the flux field repeatedly scans the nonmagnetic surface.

In a particular embodiment of such a device the invention provides a magnetic printing and/or display device comprising apparatus for dusting the movable magnetizable surface of the device with magnetic powder, the apparatus including a substantially horizontal nonmagnetic tube, a magnetic rotor inside the tube whose axis of rotation is parallel with the tube, the rotor producing a system of magnetic flux at the outer surface of the tube which is divergent in a plane perpendicular to the tube axis, and a substantially horizontal nonmagnetic ledge extending substantially tangentially from the outer surface of the tube to adjacent the magnetizable surface, the arrangement being such that rotation of the rotor in a given direction causes a layer of magnetic powder from a supply of the powder to creep up the outer surface of the tube in the opposite direction and across the ledge by somersaulting of the powder as the divergent flux system repeatedly scans the outer surface of the tube.

BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the invention will now be described with reference to the accompanying drawings, in which:

FIGS. la to Is are a time sequence of events which help to explain the principle on which the invention is based.

FIG. 2 illustrates a simple extension of the principle described with reference to FIGS. Ia to 1e;

FIG. 3 is a schematic representation of a magnetic printing and/or display device incorporating the invention; and

FIG. 4 is a cross-sectional view of the device of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. la to 1e, which represent successive moments in time, a nonmagnetic support I has on its upper sur-. face '2 a small quantity of magnetic powder 3. A bar magnet 4 disposed below the support I gives rise to a divergent system of magnet flux 5 above the surface 2.

In the following, the effect of moving the magnetic below and parallel to the underside of the support will be described. The magnetic force on the powder can be resolved into two components; a horizontal component parallel to the surface 2 acting" towards the axis of the magnet, and a vertical component acting perpendicularly upwards relative to the surface 2. It isessential for carrying out the invention that the horizontal component is never sufficiently large to cause bulk movement of the powder along the surface 2 with the magnet; in other words it must be no greater than the friction, which is itself enhanced by the vertical component, between the powder and the surface. This condition can be satisfied by choosing a magnet of appropriate strength in relation to its distance belowthe surface 2, and the surface 2 can be artificially roughened to provide a better keying of the powder into the surface,

In FIG. la, the magnet is sufficiently for from the powder 3 that the powder is not appreciably disturbed by the magnetic flux, but as the magnet is moved parallel to the underside of the support 1 in the direction A it eventually reaches the position shown in FIG. lb at which the magnetic powder forms into filaments which align themselves along the lines of flux, i.e., pointing away from the magnet.

Further movement brings the magnet directly below the powder 3, the filaments then pointing upwards, FIG. 1c, and as the magnet moves away from the powder the filaments bend in the opposite direction keeping themselves aligned with the magnetic flux, FIG. 111. At the position shown in FIG. Ie the magnet is once again sufficiently far from the powder 3 not to appreciably disturb the latter.

It will be seen that as the magnet moved in the direction A from left to right the powder filaments rotated in the opposite direction, and the quantity of powder 3 will in effect have movedto the left by an amount approximately equal to the length of the filaments. This phenomenon will be referred to herein as somersaulting of the magnetic powder.

If the sequence described above is performed repeatedly, the magnet 4 each time being returned to its original position of FIG. la without further disturbing the powder on its return, the repeated scanning of the surface 2 in the same direction by the divergent flux system 5 will cause the quantity of powder 3 to creep along the surface in the opposite direction.

Asimple extension of this principle is shown in FIG. 2, in which the surface 2 is covered with a layer 6 of magnetic powder, and the magnet 4 is elongated to extend across the width of the support.

In this case movement of the magnet in the direction of the arrow B will cause an associated localized elongated region of disturbance 7 to traverse the layer of powder, the end result being that the layer of powder will have moved a small distance along the surface in the opposite direction to the direction of movement of the magnet.

If th'e'surface 2 is repeatedly scanned in the same direction by the elongated divergent system of magnetic flux produced by the magnet 4, the layer of powder 6 will creep along the surface'in the opposite direction, the effect thus being similar to that 'described with reference to FIGS. Ia to Ie. In either case, it is of course not necessary that the repeated scanning be performed each time by the same magnet: a number of different magnets can be used successively. f

An embodiment of a magnetic printing and/or display device'incorporating the invention will now be described with reference to FIGS. 3 and 4. The figures are not to scale and are only intended as a schematic illustration of the relevant parts of the device.

The device includes a drum 10 which is mounted in the opposite walls 16 of the device housing for rotation about an axis l I. The cylindrical surface 12 of the drum is magnetizable and constitutes the surface on which matter to be printed and/or displayed is recorded as the drum rotates by a stationary set of recording heads (not shown).

Beneath the drum lies a trough 13 into which a supply of magnetic powder 14 can be introduced via the hopper 15, the endwalls of the trough being formed by the walls 16 of the device. A nonmagnetic tube 17 is disposed horizontally along the trough. The tube may be made of aluminum, and at each end meets the respective walls 16 so that magnetic powder in the trough cannot enter the inside of the tube. A horizontal nonmagnetic ledge 18 extends tangentially from the top of the tube to below the drum 10, adjacent the cylindrical surface 12.

A magnetic rotor 19 is located inside the tube 17 for rotation about an axis 20 parallel with the tube. The rotor comprises a plurality of mutually parallel bar magnets, such as 21, which are disposed side-by-side with their like poles adjacent, so effectively forming a flat rectangular magnet magnetized from edge to edge in a direction perpendicular to its axis. Each edge of the rotor produces at the outer surface of the tube 17 a system of magnetic flux which is divergent in a plane perpendicular to the tube axis (FIG. 4). In some cases it may be preferable to join the tips of the bar magnets by soft metal pole pieces in order to even out the flux distribution.

The arrangement of the apparatus shown in FIGS. 3 and 4 is such that, according to the principle discussed with reference to FIGS. 1 and 2, rotation of the rotor in the direction of the arrow B (FIG. 4) causes a layer of powder 22 from the supply 14 to creep in the direction of the arrow C up the convex outer surface of the tube 17 and across the ledge 18, bysomersaulting of the powder as the flux system repeatedly scans the outer surface. Each grain of powder is held in position on the tube by the attraction of its circumferential neighbors, but to assist somersaulting up the side of the tube it may be necessary to artificially roughen the outer surface. We have found that rubbing the outer surface of the tube longitudinally with a medium grade emery paper gives a suitable surface.

As well as causing the layer 22 to creep up the outer surface of the tube, the arrangement described also causes the layer to spread along the length of the tube, so that the trough need only be filled at one end. This is accomplished via the hopper as described previously.

The drum l0 rotates, in the direction of arrow D, in brushing contact with the layer of powder on the ledge. Thus the magnetized regions on its surface 12 become dusted to form a powder image of the matter for printing or display. In the embodiment described, the purpose of the ledge 18 is to allow the drum to be offset from the tube I7 so that the magnetic rotor 19 does not affect the selective magnetization on the surface 12. Any powder which is not picked up by the magnetizable surface of the drum l0 falls over the edge of the ledge 18 and is thus returned to the supply in the trough 13.

It is to be understood that the foregoing description of specific examples of this invention is not to be considered as a limitation ofits scope.

Iclaim'.

ll. In a magnetic printing and/or display device, apparatus for dusting the movable magnetizable surface of the device with magnetic powder comprising a convex nonmagnetic surface extending from a supply of the powder to a nonmagnetic ledge adjacent the magnetizable surface, and a magnetic rotor disposed behind the nonmagnetic surface and having its axis of rotation parallel thereto for producing at the nonmagnetic surface a system of magnetic flux which is divergent in a plane substantially perpendicular to the axis of rotation, the arrangement being such that rotation of the rotor in a given direction causes a layer of magnetic powder to creep in the opposite direction along the nonmagnetic surface and across the ledge by somersaulting of the powder as the flux field repeatedly scans the nonmagnetic surface.

2. In a magnetic printing and/or display device, apparatus for dusting the movable magnetizable surface of the device with magnetic powder comprising a substantially horizontal nonmagnetic tube, a magnetic rotor inside the tube whose axis of rotation is parallel with the tube, the rotor producing a system of magnetic flux at the outer surface of the tube which is divergent in a plane perpendicular to the tube axis, and a nonmagnetic ledge extending substantially tangentially from the outer surface of the tube to adjacent the magnetizable surface, the arrangement being such that rotation of the rotor in a given direction causes a layer of magnetic powder from a supply of the powder to creep up the outer surface of the tube in the opposite direction and across the ledge by somersaulting of the powder as the divergent flux system repeatedly scans the outer surface of the tube.

3. Apparatus according to claim 2 wherein the magnetic rotor is a flat rectangular magnet magnetized from edge to edge in a direction perpendicular to its axis of rotation.

4. Apparatus according to claim 3 wherein the flat rectangular magnet comprises a plurality of mutually parallel bar magnets disposed side-hy-sidc with their like poles adjacent.

5. Apparatus according to claim 4 wherein the tube is disposed along a trough in which the supply of powder is contained.

6. Apparatus according to claim 5 wherein the magnetizahle surface is the cylindrical surface ofa drum, the axis of rotation of the drum being vertically offset from that of the rotor. 

1. In a magnetic printing and/or display device, apparatus for dusting the movable magnetizable surface of the device with magnetic powder comprising a convex nonmagnetic surface extending from a supply of the powder to a nonmagnetic ledge adjacent the magnetizable surface, and a magnetic rotor disposed behind the nonmagnetic surface and having its axis of rotation parallel thereto for producing at the nonmagnetic surface a system of magnetic flux which is divergent in a plane substantially perpendicular to the axis of rotation, the arrangement being such that rotation of the rotor in a given direction causes a layer of magnetic powder to creep in the opposite direction along the nonmagnetic surface and across the ledge by somersaulting of the powder as the flux field repeatedly scans the nonmagnetic surface.
 2. In a magnetic printing and/or display device, apparatus for dusting the movable magnetizable surface of the device with magnetic powder comprising a substantially horizontal nonmagnetic tube, a magnetic rotor inside the tube whose axis of rotation is parallel with the tube, the rotor producing a system of magnetic flux at the outer surface of the tube which is divergent in a plane perpendicular to the tube axis, and a nonmagnetic ledge extending substantially tangentially from the outer surface of the tube to adjacent the magnetizable surface, the arrangement being such that rotation of the rotor in a given direction causes a layer of magnetic powder from a supply of the powder to creep up the outer surface of the tube in the opposite direction and across the ledge by somersaulting of the powder as the divergent flux system repeatedly scans the outer surface of the tube.
 3. Apparatus according to claim 2 wherein the magnetic rotor is a flat rectangular magnet magnetized from edge to edge in a direction perpendicular to its axis of rotation.
 4. Apparatus according to claim 3 wherein the flat rectangular magnet comprises a plurality of mutually parallel bar magnets disposed side-by-side with their like poles adjacent.
 5. Apparatus according to claim 4 wherein the tube is disposed along a trough in which the supply of powder is contained.
 6. Apparatus according to claim 5 wherein the magnetizable surface is the cylindrical surface of a drum, the axis of rotation of the drum being vertically offset from that of the rotor. 